Vacuum tube circuit



Oct. 9, 1934. R. D. DUNCAN, JR 1,975,834

VACUUM TUBE CIRCUIT Filed oct. 20. 1923 3' sheets-Sheet 2 INVENTOR Faber ancan, fr. I

R. D. DUNCAN, JR'

VACUUM-TUBE CIRCUIT V Filed 001'.. 20. 1923 v I5 Sheets-Sheet 3 ATTORNEY Patented Oct. 9, 1934 VACUUM TUBE CIRCUIT A 'Robert D. Duncan, Jr., East Orange, N. J., as-

signor, by mesne assignments, to Wired Radio,

Inc., New York, N. Y., a corporation of Delaware Application october zo, 1923, serial No. 669,662'

9 Claims.

This invention has to do with the operation of electron discharge devices, in signaling systems, on alternating current, and its object is to provide an enicient circuit arrangement whereby the fila- 5'; ment of such a device can be heated by alternating lcurrent with little or no resulting low frequency component in the Voutput circuit of the device.

In theuse of alternating current for the pur- 10`;pose stated it has heretofore been the practice to employ what is known as a center point connection from the secondary winding of the filament transformer to the grid or plate or boththe idea being to prevent any fluctuating differ- 1a5 i; ence of potential between the lament and either of. the other electrodes. I

In the practice of the present invention an alternating potential of the same frequency as the filament heating current is applied to one or gqjboth of thefcold electrodes and the intensity and sometimes the phase relation. of the potentialsv thus applied are so proportioned that the alternating current lhum which. would otherwise bepresent in large Volume in the output circuit is gijsubstantially or completely neutralized.

Generally the filaments of `electron discharge devices (vacuum tubes) are designed to operate on relatively low voltage,say 6 volts, and in order to enable them to be'operated from the ordinary 3:1;110 volt lighting circuits in common use, it is necessary to employ a stepdown transformer.

According to the preferred practice of the present-invention, a transformer comprisingV one or more secondary windings in addition to the usual 35,;secondary winding is employed. The additional or supplementary winding or windings arerinter'- posed in'the circuit'between one side`of thelament and the grid or plateor both, as the casey may be, and are -designed to` produce the proper 4g alternating potential or,A potentials which, whenI applied to the respective electrodes, will produce the desired neutralizing effect. required f or this Ypurpose foreach particular type of yvacuumtube are-best determined by experi- 45, `gment. v

,It is not necessary thata special transformer Vhaving more than one secondary winding be emv taryiwindingand havingxone ormore adjustable' 55S air gaps in .the. magnetic; core, thereof has been- The potentials found to be particularly effective on account of. the facility afforded for accurately adjusting the inductive coupling between the primary andl secondary winding or windings, thus affording a convenient means for adjusting the intensityof the potentials impressed on thegrid or plate or both.

A clearer understanding ofr the invention'may. be had fromthe following detailed descriptionin con-junction with the accompanying drairvings:` in which v v Fig. i shows anamplier circuit comprisingy two three-electrode vacuum tubes with their iilamentsv arranged. to be heated by alternating current, there being provided a transformer having a, 70 primary and two secondary windings. In this. circuit the potential developed by the additional or supplementary secondary windingisimpressed; on both the grids and plates of the two vacuumV tubes;

Fig. 2 is a circuit similar to Fig. 1 wherein only the platesv of the vacuum tubes-are connected. with the supplementary secondary winding;

Fig. 3 isa modification ofthe. circuit shown in; Fig. 1 wherein the grid and plate connections to the supplementary secondary winding are effected through the media of potentiometers connected across the terminals of the supplementaryl secondary winding; Fig. 4 is a modification of the circuitshown in Fig. 2 wherein'the plate connections of the suppleinentary winding Yof, the! transformer are ef-j fected through the medium of a vpotentiometer connectedacross theLterminals of the supplementary winding;

Fig. 5 shows a single-tube receiving circuit comprising two transformers, one of which is pro-Y vided for stepping down thel voltage for the lament, and theother for furnishing the alternating potential for application to the grid and' plate;

` Fig.'6 is a two-tube ampliiier'circuit compris` ing a transformer having two supplementary seco ndary windings, one of which i'sA intended lto furnish the alternating potential to be applied. to the-grids, while-the-other is intended-to2 furnish the alternating-potential to be applied to.` the plates; and

Fig. 7 is a single-tube receiving 'circuit' com-v prisinga transformer having adjustable air gaps.I

Intheamplier-circuit of Fig. .1, the trans-fr` former 1. comprisesr primary winding 2, which may be associatedfthrough its terminals with an ari-r, tenna'or` metallic transmission linefor receiving.`

incoming signals, and asecondary--winding 3l isi- 1105 connected in the input circuit of vacuum tube 4. Each of the vacuum tubes 4 and 5 comprises a filament or cathode 6, grid or control electrode '7, and plate or anode 8. The filaments 6 are connected in parallel to the terminals of the secondary winding 9 of the transformer 10, the primary 11 of which is connected to an alternating current source -12. The transformer is provided with an additional or supplementary winding 13 of a suitable number of turns which may be determined by experiment. One terminal of the supplementary winding l; is connected to .one side of each of the filaments, and the other terminal is connected through batteries 14 and 15 to the grids and plates respectively. The output circuit of vacuum tube 4 is associated with the input circuit of vacuum tube 5 through the medium of transformer 16, which functions in the wellknown manner to pass the output of tube 4 to the input of tube 5. The aniplied output of tube 5 is passed through transformer 17 to any suitable indicating device or detector. The transformers 1, 16 and 17 may be either of the audio frequency or radio frequency type, depending upon whether the circuit shown is intended to operate as an audio frequency'or radio frequency amplifier.

It is well known that to light the filaments of vacuum tubes in a receiving circuit by alternating current Without suitable provision for neutralizing the efects'of lthe alternating current results in the production of a hum in the indicating device whichV will substantially, if not completely, render the incoming signals indistinguishable. By means of the supplementary secondary winding 13 an alternating potential of predetermined intensity and of the same Afrequency as that of the source l2 is impressed upon both the grids 'l and plates 8. This potential, which, for convenience, may be referred to as the control potential, operates effectively to neutraliZe the alternating current hum in the output circuits of the vacuum tubes. It has been found that generally a supplementary secondary winding having approximately half the number of turns of the main secondary winding 9 will produce the desired effect. It is preferable that the windings 9 and Y1.", be connected differentially as indicated. The control potentials as applied to the grid or plate should, generally, be exactly 180 out of phase with the potential developed by the secondary I'winding 9 at the terminal to- Which the supplementary winding 13 is connected. In some instances, it may be necessary to correct the phase relations by the insertion in the circuit of suiti able capacity or inductance, but it has not been found necessary to resort to this expedient in the experiments heretofore conducted.

The circuit of'Fig. 2 differs from that Yof Fig.

1in that the plates, only, are connected to the supplementary secondary winding, while the grid circuits are connected to the respective filaments in the-usual manner. j In arrangements such as that'of Fig. 2, it is usually necessary to make the supplementarywinding 13 `Aof a .large number of turns, the number being dependent upon the amplificationfactor of the tubes. For example, if a control potential E applied to the grids would be effective to neutralize the alternating current jhum when the amplification factor of the tube is 5,' av control potential of 'approximately 5E would berequired to be impressed upon the plates in orderto produce the same result. Where, however, the control potential is applied to both the '.grid and p1atea vmore'complex situation arisesl on account of neutralization being effected at both cold electrodes.

The arrangement of Fig. 3 is basically similar to that of Fig. 1 in that alternating control potentials are applied to both the grids and plates. For effecting adjustments of the control potential potentiometers 18 and 19 are connected across the terminals of the supplementary secondary winding 13. Each of these potentiometers is provided with two adjustable contacts which are connected respectively to their associated grids and plates. The applied control potential may thereby be separately adjusted for both grids and both plates. Each of the grid circuits is provided in this case with a biasing battery 20 and potentiometer 21.

The circuit arrangement of Fig. 4 is basically similar to that ofv Fig. 2 in that the alternating control potentials are applied to the plates only. This circuit is also similar to that of Fig. 3 in that a potentiometer 22 having two movable contacts is connected across the terminals yof the supplementary secondary winding 13. Y

The single-tube receiving circuit of Fig. 5 is provided with two transformers 23 and 24 each 100 havinU a single primary and a single secondary winding. In the particular arrangement shown4 the number of turns of the secondary windings utilized is variable, but this feature is not at all essential to the proper operation of the circuit. 105 The function of the secondary winding 25 of transformer 24 is the same as that of the supplementary secondary winding 22 of Fig. 4. By the provision of movable contact 26 for effecting connection with a variable number of turns of 110 the secondary 25 and the provision of potentiometer 27, a Wide range and great fiexibility of adjustment of the alternating control potential is afforded.

In the circuit of Fig. 6 the transformer is pro- 115 vided with two supplementary secondary Windings 13 and 28, the first of which provides an alternating control potential for the plates, and the latter alternating control potential for the grids. It is desirable with this arrangement to 120 provide a potentiometer 29, which is shown connected across the terminals of theV supplementary secondary Winding 28 for adjusting the alternating control potential applied to the grids. Another potentiometer similar to 29 may likewise be 'connected across the terminals of the supplementary secondary Winding 13 for adjusting the alternating control potential applied to the plates. Such provision, however, is not at all necessary and is not shown. The circuit of Fig. 130 6 is characterized by a high degree of flexibility, as well as simplicity, and excellent results have been obtained therewith.

Fig. '7 shows a single-tube receiving circuit comprising an iron core transformer 30 in which 135 the transformer is provided with two air gaps 31 and 32 and a pair of adjusting studs`33 and 34, whereby the widths of the air gaps may be adjusted. By Varying the widths of the air gaps the inductive coupling between primary winding 140 11 and the tWo secondary windings 9 and 13 may be adjusted, therebyl effecting adjustment of the induced potentials in the secondary windings. The various connections are similar to those pre- Viously shown and described, andthe operation145 of the circuits is lthought to be apparent.

I claim: i l l 1. A system comprising an electron discharge device including anode, cathode and control electrode, an input circuit and-an output circuit forn4 @Q1-'of said secondary windings having one of its said device, a lsource of alternating current for heating said cathode,a transformer comprising a primary winding andtwo fsecondaryfwindings, said' source ciy alternatingv current :being-*cone nected .to said primary winding, said -cathode :being connected across ytheterminals of one'ofY said secondary windings, `and the terminals ofthe other of said secondary windings Abeingsoconnectedztosaidzcathode and to one of the other of said electrodes respectively that the phase opposition of the two said secondary windings tends to eliminate the effect of alternating current ripple in the output of said electron discharge device.

2. A system comprising an electron discharge device including anode, cathode andcontrol electrode, an input circuit and an outputl circuit for said device, a source oi alternating current for heating said cathode, a transformer comprising a primary winding and a secondary winding, said source of alternating current being connected to said primary winding, said cathode being connected across the terminals of said secondary winding, and a coil arranged in inductive relation to said alternating current source, one terminal of said coil being connected to said cathode and another terminal of said coil being connected to one of the other of said electrodes, said coil and its connections being characterized in that a current may be derived therefrom which when applied to said electron discharge device tends to neutralize the ripple-eiect due to the alternating current by which said cathode is heated.

3. A system comprising a three-electrode electron discharge device including anode, cathode and control electrode, an input circuit and an output circuit for said device, a source oi alternating current for heating said cathode, a transformer having a primary winding and two secondary windings, said source of alternating current being connected to said primary winding, said cathode being connected across the terminals of one of said secondary windings, the other of said secondary windings having one of its terminals connected to said cathode, a resistance element connected across the terminals of the last-mentioned secondary winding, and an adjustable connection to said resistance element, said adjustable connection being connected with one of said electrodes other than said cathode.

4. A system comprising a three-electrode electron discharge device including anode, cathode and control electrode, an input circuit and an output circuit for said device, a source of alternating current for heating said cathode, a transfl former having a primary winding and two secondary windings, said source of alternating current being connected to said primary winding, said cathode being connected across the terminals of one of said secondary windings, the other terminals connected to said cathode, a resistance element connected across the terminals of the last-mentioned secondary winding, and a pair of independently adjustable connections to said resistance element, each of said adjustable connections being connected to different ones of said electrodes other than said cathode. 5. A system comprising a three-electrode electron discharge device including anode, cathode and control electrode, an input circuit and an output circuit for said device, a source of alternating current for heating said cathode, a transformer having a primary winding and two second- ;giary windings, said source of alternating current bei-ng l connected,A fto said'y primaryWinding, said cathode being connectedacross thezterminals, of one of-saidfsecondary windingsg, the other of said secondary-,windings being. connected .tov said cathode and' at least one ,ofthe` other of said `electrodes jointly,.and meansior varying, theinductive .coupling between said primary winding Aand ats-leastz one.,` of said .secondary windings;y said means being-v; characterizedvin lthat vit- .enables the ripple eiect in said output circuit to be substantially neutralized upon proper adjustment of said inductive coupling and'of the phase relation between the connections of said secondary windings, which ripple eect would otherwise result from a variation of control electrode bias with respect to the alternating potential applied to said cathode.

6. A system comprising a three-electrode electron discharge device including anode, cathode and control electrode, an input circuit and an output circuit for said device, a source of alternating current for heating said cathode, a transformer having a primary winding and two secondary windings, said source of alternating current being connected to said primary winding, said cathode being connected across the terminals of one of said secondary windings, the other of said secondary windings being connected to said cathode and at least one of the other of said electrodes jointly, and means for varying the inductive coupling between said primary winding and said secondary windings, said means being characterized in that it enables the ripple eifect in said output circuit to be substantially neutralized upon proper y adjustment of said inductive coupling and of the phase relation between the connections of said secondary windings, which ripple eifect would otherwise result from a variation of control electrode bias with respect-to the alternating potential applied to said cathode.

7. A system comprising a three-electrode electron discharge device including anode, cathode and control electrode, an input circuit and an output circuit for said device, a source of alternating current for heating said cathode, an iron core transformer comprising a primary winding and two secondary windings, the core of said transformer being provided with at least one adjustable gap, means for adjusting the width of said gap whereby the inductive coupling between said primary winding and at least one of said secondary windings may be varied, said source of alternating current being connected to said primary winding, said cathode being connected across the terminals of one of said secondary windings, the other of said secondary windings being connected to said cathode and at least one of the other of said electrodes jointly.

8. The combination with an electrical discharge device having a cathode adapted to be heated, a cooperating anode and a discharge controlling grid, of a source of alternating current, a potentiometer associated with said cathode, circuit elements for impressing across said cathode and potentiometer an alternating potential derived from said source, external circuit connections including said potentiometer between said cathode and anode and between said cathode and grid, means including a transformer having two secondaries whereby compensating currents in phase opposition to one another may be impressed upon the electrodes of said electron discharge device, and means for independently adjusting the connections of the anode and grid to the cathode lthrough said potentiometer to compensate for ary windings, a potentiometer, said cathode and at least one other electrode of said thermionic tube being adjustably connected to said poten` tiometer and said potentiometer being connected across the termnaisof another of said secondary windings whereby the ripple effect otherwise occurring in the output circuit of said apparatus may be eliminated.

ROBERT D. DUNCAN, J R. 

